In a fixing apparatus in the past, a sheet is heated by a heater. However, the temperature of the heater in a portion where the sheet does not pass excessively rises. Therefore, problems such as a warp of the heater, deterioration of a fixing belt, and speed unevenness due to expansion of a conveying roller sometimes occur. It is undesirable from the viewpoint of energy saving to heat the portion where the sheet does not pass. Therefore, it is an important technical subject from the viewpoint of environmentally to intensively heat only a portion where the sheet passes.
Further, necessary to provide a temperature sensor to grasp a heat generation state of a heating roller and perform temperature control. However, to perform accurate temperature control, necessary to perform wiring in a state in which a circuit for power feed to the heater and the temperature sensor are completely insulated from each other.